Why does it matter if a 350 have 7a, 7, 6, or 5 heads on it. With the exception of just someone personal preference. Since motors can be rebuilt to whatever specs. For instance, my 72 cs engine will be rebuilt to the same specs as a 70 motor.

 

For one thing, the 7a heads and I beleive the 7 heads came with hardened valve seats.

 

It really doesn't matter too much since the heads are very close to each other performance wise. What you need to be aware of is the later heads have rotators on the valves, which means deeper spring pockets. Can't remember the specifics right off but maybe 7 was on exhausts only and 7a were on both? Again, doesn't matter that much but is a consideration when buying valves and springs.

 

All SBO heads prior to the No 8 heads that came out with the 1973 model year are equivalent in flow and performance potential. You may find slightly different numbers on the web for chamber volume or port flow, but the reality is that these numbers are typically based on a sample size of one or two castings and don't represent a statistically valid number of samples. These heads all had chambers with a design volume of about 64cc. As-cast volumes vary by several ccs and were usually on the large side from the factory. Similarly, if the heads have ever had the valves cut or the deck milled, chamber volume will vary.

The "hardened seats" were factory issue for all Olds heads from the 1971 model year on. Understand that these are NOT press-in hardened steel seats. They are a thin layer of induction-hardening in the parent cast iron. The first time the valve seats are cut, that hardening layer is removed.

 

I have the 7a heads on my 350 and I was going pull the heads off and get them refurbished, which I assume would include cutting/lapping the valve seats. Does the machine shop typically add the press-in seats to the process?

 

Not unless you tell them to and pay extra. Also, DO NOT let them install Chevy seats. The Chevy seats are too tall and if the heads are cut for them, the shop will break through into the water jacket and the heads will be junk. Be sure to use Olds-specific steel seats.

 

Yike! Glad I asked!

 

Also make sure enough clearance is used on the center exhaust guides, somewhere around .0024" is needed I believe. A few have had those valves stick in fresh heads.

 

64 cc as cast? Me thinks 68-69cc as cast is a lot closer. Agree with everything else you posted.

 

Actually, I said 64 as-designed, and a few CC larger as-cast. I agree that 68-ish is probably the average as-cast number.

 

So the stories about the #5 heads being the best for a SBO is untrue? 5,6,7,&7a are all pretty much the same in stock form?

Eric

 

#4 are 64cc as cast and are the best SBO head in stock form. Flow potential all the same on all the SBO heads 1967-1972. #5 are the most common and easy to find because they were used for 2 model years.

 

I was on summit racing website looking at each olds 350 heads from 68-72 and notice all were priced the same pretty much. Are they all the same or is each year build to factory specs?

 

Dave picked the #4, I assume, because the 330 heads are smaller chamber volume otherwise nearly indentical to the later 5,6,7,7A heads. One area that may be an issue is the change in cam bank angle, some claimed the 67 330 changed to the newer 39 bank angle. The earlier 330 heads all were designed for 45 degree can bank angles, #1 had unique and impossible to find replacements, rocker shafts and number 2 heads had 3/8" stud non adjustable rocker arms. Number 3 heads were like later heads except having possible pushrod interference on a later motor. Summit racing would have nothing but Edelbrock heads with big 77cc chambers.

 

The only effect that lifter bank angle has on the heads is the pushrod clearance hole. You can easily open that hole up for more clearance if needed.

 

#4 330 heads are from 39 deg bank angle engines. 1,2 & 3 are SBO heads from 45 deg bank angle engines.

 

I have heard both, wasn't there a mid year change? I have never owned a 67 330.

 

I should have been clearer on how to fix the issue. Doesn't a grinder fix everything on iron heads.